Lubricating oil composition



Patented Apr. 25, 1944 LUBRICATING OIL C QMPOSITION Willard L. Finley, Edgewood Arsenal, Md., as-

signor to Sinclair Refining Company, New York. N. Y., a corporation of Maine No Drawing. Application August 15', 1941, Serial No. 407,002

Claims.

My invention relates to improvements in compounded petroleum lubricating oils. The improved lubricating oil compositions of my invention consist essentially of a petroleum oil base where R. is a branched chain aliphatic group containing at least six carbon atoms, for example the 2,ethyl hexyl group, or the 2,ethyl butyl group. These compounds may be less accurately but more conveniently described as calcium isoalkyl salicylates. For convenience hereinafter, they will frequently be so described, the specific illustrative compounds above mentioned being referred to as calcium iso-octyl salicylate and calcium iso-hexyl salicylate, respectively.

The trend of development in internal combustion engines has imposed increasing burdens upon the oils used for their lubrication, particularly with respect to the operating temperatures and pressures. Extreme requirements in both of these respects are represented by the Diesel type of engine and supercharged aircraft engines. The

useful operating life of a lubricating oil, in such severe services, is determined in a large measure by its thermal stability and by its physical capacity to continue functioning as a lubricant at the high temperatures and pressures encountered. One measure of thermal stability is resistance to oxidation. Oxidation promotes eftherthe formation of sludge or the formation of acids corrosive to hearing metals, or both. However, in another aspect the effect of thermal stability is determined not only by the extent of oxidation or decomposition but also by the character of the products of such decomposition or oxidation and by the extent and location, within the engine, ofdeposits of such products.

The improved lubricating Oil compositions of my invention have, in addition to the lubricating properties of the petroleum oils of which they are compounded, a high solvent capacity for sludge '01 the 'character formed by oxidation of petroleum lubricating oils, and, perhaps of even greater importance, the property of rendering deposits of sludge and carbon" within the engine soft and friable rather than hard and coherent and of disintegrating and removing such deposits as an incident of the normal operation of the engine. In engines of this type the high temperature to which lubricating oil is subjected, particularly at the top of the stroke, frequently causes deposition of sludge and carbonization in the groove for and behind one or more of the piston rings. Consequent sticking Of the rings rapidly deprives the piston and cylinder wall of proper lubrication inducing excessive wear and, frequently, scoring of the cylinder wall. The formation of such carbon" deposits, hard enough and coherent enough to involve sticking of the rings is materially retarded, if not avoided, by the-use of the improved lubricating oil compositions of my invention.

In the lubricating oil compositions of my invention the calcium iso-alkyl salicylates function not only to inhibit sludge formation and to modify. the character of the carbon deposits, but they also function as strong anti-oxidants effec'tive to inhibit, at least over a prolonged induction period, the rate of oxygen absorption at elevated temperatures, thus rendering such lubricating oil compositions non-corrosive, or less corrosive, to alloy bearing metals. While these addition agents do not materially increase the film strength of a base oil in which they are incorporated, they are compatible with known film strength agents such as chlorinated diphenyl, brominated diphenyl, suiphurized sperm oil, and the like. In lubricating oil blends including such film strength agents, thecalcium iso-alkyl salicylates efiectively inhibit the pro-oxidant eifect that many of these known film strength agents exert.

In my co-pending application Serial No. 368,992, filed December 7, 1940, I have disclosed lubricating compositions including as addition agents various calcium salts of the normal alkyl esters of salicylic acid. However, I have found that a. lubricating composition includin the calcium salts of an iso-alkyl ester of salicylic acid is in several respects superior to a lubricating composition comprislng the same base oil and thecalcium salt of the corresponding normal. ester, particularly for service under extremevv tempera-- ture conditions. This superiority apparently is due to the greater thermal stability or the calcium iso-alkyl salicylates. These salts have the further economic advantage of being less costly.

Under moderately severe temperature conditions, the addition agents of my present-invention are at most only slightly less effective as oxidation inhibitors than are the calcium salts of the normal alkyl esters of salicylic acid. This is well illustrated by comparison of the results. of oxygen absorption tests at 400 F. on three samples each using as the base oil a. Pennsylvania lubricating stock having a gravity of 28.1 A. P. I. and a Saybolt viscosity of 560.0 seconds at 100 F. and 69.3 seconds at 210 F. One of these samples contained no addition agent. It absorbedoxygenunder the test conditions at a substantially constant rate of approximately 21.5 cc. per minute per 100 grams of oil. Incorporation of 3.5% of calcium 2,ethyll1exyl salicylate in a fresh sample of the same base oil reduced the rate of oxygen absorption under the same test conditions to 6.6 cc. per minute per 100 grams of oil over an induction period of 175 minutes duration. salicylate in a fresh sample of this same base oil reduced the rate of oxygen absorption under the same test conditions to 5.9 cc. per minute over an induction period of 212 minutes duration.

However, when fresh samples of these two compounded oils were first heated at 500 F. for 45 minutes and then subjected to the oxygen absorption test at 400 F., the induction period for the blend containing the normal alkyl salicylate had decreased from 212 to 112 minutes, whereas the induction period for the blend containing the iso-alkyl salicylate had decreased from 175 minutes only to 156 minutes. The greater thermal stability of a blend containing the iso-alkyl salicylate as compared to that containing the corresponding normal salicylate is also made evident by the greater effectiveness of the addition agent in the former in increasing the Indiana sludging time, and by the further circumstance that when fresh samples of both blends had been heated at 500 F. for 45 minutes and then cooled and filtered the blend containing the iso-alkyl salicylate was found to have lost only 21% of its available calcium whereas the blend containing the normal alkyl salicylate had lost 42% of the oil-soluble calcium. Further advantages to be derived from thegre ater thermal stability of the lubricating'compos'itions of my invention, even under less severe temperature conditions, are incheated by the fact that in'the Indiana oxidizer test at 341? F., a blend containing 3.5% of calcium n-octyl salicylatev precipitated and became cloudyafter 60 test hours; whereas a blend containing 3.5% Iof calcium iso-octyl salicylate in thesameibas'ejoil, in this instance a blend com prising 70% ,solvent treated Mid-Continent neutral and"30% Pennsylvania bright stockv remained clear for 420 hours.

In service 'as a lubricant in internal combustion engines where the .maximum oil film temperature approximates 500 F., although the main body, of the lubricant is at a considerably lower temperature, the greater thermal stability of the lubricating compositions of the present invention makes "itself evident in the form of further improvements in the cleanliness of the engine, both as. to lacquer-like deposits on the piston skirt andring lands, sludge deposits on the underside of the'piston crown, and as to depositslof sludge and carbon on the piston above the top' ring," on the rings, and in the ,ring

grooves; the last-mentioned factorbeing of major,

importance in ftheprevention of ring sticking.

In' the lubricating compositions of my .inven tion the effectiveness of the addition agent, in in- Incorporation of 3.5% of calcium n-octylf creasing the sludging time'and the duration of the induction period during"which the rate of oxidation is retarded, varies withthe particular addition agent selectedland with the. amount of addition agentem'ployed. Moreover, the extent of these efiects isdifierent for different base oils. Within reasonable limits the extent of these effects, is in general increased as the amount of the addition agent is increased.

' covered in the distillate) and .46 pound of The tests recorded in the following table will serve to illustrate the relative effectiveness of calcium iso-hexyl salicylate and calcium isooctyl s'alicylate on the Indiana sludging time of a given base oil, the oil in this instance being an S. A. E. 30 Pennsylvania type petroleum lubricating oil having a gravity of 28.3 A. P. I. and Saybolt viscosities of 563 seconds and 67.8 secends at F. and 210 F., respectively.

The effect of varying the proportion of the addition agent, and the relative effectiveness of the calcium salts of the corresponding normal and iso-alkyl esters of salicylic. acid are illustrated by the results of the tests recorded in the following table. The Pennsylvania type base oil used in the tests recorded inthe following table was the same as that used in the tests previously described. The other base oil was a petroleum lubricating oil having an S. A. E. rating of 40 derived from a South Texas crude. This base oil had a gravity of 19.7 A. P. I. and Saybolt viscosities of 1617 seconds and 81.0 seconds at 100 F. and 210 F., respectively.

Blend com Blend con- Blend-con- Blank mining 1.33% mining 1.33% tainin 3.5%

base calcium cium um oil n-octyl iso-octyl iso-octyl salicylatc salicylate salicylate SOUTH TEXAS (S. A. E. 40)

I. S. T n 22.5 38 57! 81.0

PENNSYLVANIA s. A. a. so

1.s.r 200 366 415 I 450+ The following example will serve to illustrate the preparation of a compounded lubricant embodying the invention and. including the calcium salt of the 2,ethyl hexyl ester of salicylic acid:

A 12 ga lon bottle, in an oil bath, was charged with 34.5 pounds (.25 pound molecular weights) of salicylic acid, 39 pounds of 2,ethyl hexyl alcohol (an excess of 5% above the alcohol required for esterification and that which is usually resulphuric acid. This mixture was heated for a reaction period of 4 hours at a temperature increasing from 295 F. to 330 F., during which time water of reaction and some excess alcohol quietly distilled from the reaction mixture. The ester was cooled and washed first with water and finally with an aqueous caustic solution to remove sulphuric acid and any unreacted salicylic acid. The washed ester was clarified by passing it through a bed of filter aid. The final product was a limp liquid having the following properties:

Acid No 2 0. D. color 309 Saponiflcation number (found) 203 Saponification number (calculated) 224 The calcium salt of this ester was prepared by reacting the ester directly with calcium hydroxide in a lubricating coil. In this preparation 74 pounds (1 mol) of calcium hydroxide was suspended in 827 pounds of a Pennsylvania type petroleum lubricating oil having an S. A. E. viscosity rating of 30 and the mixture was heated to 180 F. To this suspension there was added 250 pounds of the ester prepared as just described and finally 12.5 pounds of water. During these additions the mixture was stirred vigorously. This mixture then was kept at 160-190" F. and stirred vigorously for 2 hours to complete the reaction with lime. It was then dehydrated by heating to 280 F. Filter cell was then added and the mixture was passed through a blotter press while maintaining a temperature of 200220 F. The clear 24% concentrate was then ready for dilution with additional oil to prepare the finished lubricating composition with or without the incorporation of other addition agents. The solubility of the calcium salt of the 2,ethyl hexyl ester of salicylic acid in oil is so great, even in a paraflin-type base oil, that upwards of 24% of this salt will remain completely in solution over prolonged periods of storage at 18 F.

The calcium salt of the 2.,ethyl butyl ester or salicylic acid was prepared from 2,ethyl butyl alcohol and salicylic acid using the same molecular proportions and the same procedure as those employed in the previously described preparation, with the following exception: After the finished ester was washed free of unreacted acids it was distilled at a temperature of 250 F. and pressure of 2.0 mm. of mercury. The distilled ester was a limp, water-white liquid. It had an acid number of 2.0. Its saponification number, as determined, was 241.0, as compared to a calculated saponification number of 256.

Service tests of 100 hours with an average oil temperature of 250 F. were made in a Lauson engine using as the lubricant in successive tests, (1) an uncompounded South Texas lubricating oil having a viscosity rating of SAE 40, (2) the same base oil with 3.5% of calcium n-octyl salicylate, and (3) the same base oil containing 3.5% of calcium iso-octyl salicylate. These tests showed marked superiority for both compounded oils as compared to the uncompounded oil and a distinct superiority for the blend containing the calcium iso-octyl salicylate as compared to the blend containing the calcium n-octyl salicylate. At the end of the service test in the run using the blend containing the normal salt, the piston skirt was nearly covered with a heavy red lacquer and the oil ring was partially filled withloose sludge while the underside of the piston crown carried a heavy sludge deposit. At the conclusion of the test using the blend containing calcium iso-octyl salicylate, the piston skirt was only partially covered with a light yellow lacquer. All rings were free of sludge deposits and the underside of the piston crown carried only a light sludge deposit. No rings were stuck in either of the tests using the compounded lubricants.

A similar comparison was made on a four cylinder caterpillar Diesel engine using, in two successive tests of 246 hours duration, lubricants compounded from a Pennsylvania base oil and 3.5-4.0% of calcium n-octyl salicylate and of calcium iso-octyl salicylate, respectively. At the conclusion of the first of these tests, using the normal salt as the addition agent, one ring was distinctly-sluggish and the piston had a hard carbon deposit above the top ring. The first ring groove of each piston contained a deposit of hard carbon and the upper ring lands were covered with a deposit of dark carbonized lacquer. On the second test, only a light carbon deposit occurred above the top ring and all rings were perfectly free. The carbon deposits in the first ring groove and on the upper lands was noticeably lighter than in the preceding test.

Additional comparative tests were made on a supercharged Waukesha engine using as the lubricants in two successive tests compounded lubricants in which the base oil consisted of a double solvent treated Pennsylvania lubricating stock having aviscosity of approximately 120 seconds at 210 F. In the first of these tests the lubricant consisted of the above-mentioned base oil, 1% of an ester, derived from the oxidation of heavy petroleum fractions, which is generally marketed under the trade name "Alox Corporation No. 152 ester and 1% calcium noctyl salicylate. In the second of these tests the lubricant consisted of the same base oil, 1% of the above-identified Alox ester and 1% calcium lso-octyl salicylate. In the first of these tests, substantial deposits were present in the first ring groove and carbonized lacquer was present on the ring lands after 104 hours of service. In the second test, after 150 hours of service, the piston skirts were essentially clean and the carbon deposits in the ring grooves, under the piston crown, and on the ring lands, were noticeably lighter than in the preceding run.

I claim:

1. A liquid lubricating oil composition comprising a petroleum lubricating oil and a minor proportion of a calcium salt of an iso-alkyl ester of salicylic acid. I A

2. A liquid lubricating oil composition comprising a petroleum lubricating oil and 05-50% of a calcium salt of an iso-alkyl ester of salicylic acid having at least six carbon atoms in the aliphatic group.

3. A liquid lubricating oil composition compris- I ing a petroleum lubricating oil and a minor proportion 01 the calcium salt of the 2,ethyl hexyl ester of salicylic acid. 

